> While paddling home into a confused and foamy kind of 3 foot
> chop yesterday . . . I noticed that I was not really having to brace
> very much for stability (at least consciously) despite the waves coming
> from various different directions. Stability seemed to increase the
> faster the boat went, at least when I wasnt slapping down the backsides
> of the waves.

> So, my question for the lurking design gurus . . . does a kayak's
> forward movement add to its initial or final stability in any way?
> I assume most stability curves are based on a static model -- i.e.,
> assuming a boat lying still in the water. But does the movement of
> the kayak through the water create any kind of lift as the kayak begins
> to heel?

A. As I understand it: To some extent, the faster you travel forward the more stable you are, up to a certain speed where vibration, or other problems set in. You'll never paddle that fast, but a hull with an oversized motor can have these problems. Look at hydroplane racers. They can shake apart at high speeds. If you are making any forward, or backward motion, relative to the water, you should have more stability than if you are sitting still. You'll also have more steering capability, and rudders will work better.

Basically the hull is carving a groove in the water, and then sitting in that groove. These are genereally displacement hulls. A planing hull would force water off of it, and be pushed back an equal amount in return, with high speeds. This is how people stay on top of the water with water skis, and how they turn. If you can paddle fast enough to get your hull to act like a water ski, forget the olympics, go pro. While there was some discussion earlier on this list about gyroscopic effect, bicycle wheels, particularly on racing bikes, are too light to have any significant gyroscopic effect on stabilizing a bicycle. Bikes and motorbikes stay up because they are moving forward. Check some physics books for more info on this.

B: The foam and froth on the water can have an effect on stability, too. It is a well known phenomenon that the surface of the water can affect wave strength. There are several descriptions of spreading oil over the water surface to dampen wave action. We did this in a ripple tank in high school physics. Foam would have a similar effect. Lower waves, and less wave impact would make for a smoother ride, and the impression of greater stability.

C: The foaming water is going to contribute, minutely, to your floatation. Since it comes up higher on your hull it is going to change the effective center of gravity ( very slightly) and the bouyancy. These effects are probably microscopic for something the size of a kayak, but for lighter objects they can readily be seen. A neat experiment: Get some whipping cream and try to float a maraschino cherry in it. It will sink. Whip the cream until it froths. Then try to support a maraschino cherry on the froth. It may sink a little, but it should stay on top. After this, place the cherry and the whipped cream on a banana split and enjoy eating your experiment.

Paul Jacobson